The genome-wide evaluation of radiation-induced changes in gene expression has typically been evaluated using microarray analysis of total cellular mRNA, which reflects modifications in a gene's transcription. However, gene expression is dependent not only on transcriptional activity, but on a variety of post-transcriptional events that ultimately control mRNA translation. Our recent data generated using the microarray analyses of polysome bound mRNA indicate that gene translation is considerably more susceptible to radiation induced modifications than is transcription. Importantly, this study showed that there is a correlation between the genes whose translational activity was affected and the expression of their corresponding proteins. The overall goal of this proposal is to delineate the significance of radiation-induced translational control of gene expression in cellular radioresponse. Towards this end, radiation-induced translational gene expression profiles will be generated as a function of cell type. These studies will involve microarray analysis of polysome-bound mRNA isolated from tumor cell lines originating from histologies relevant to radiotherapy as well as from a variety of normal cells. This genome wide interrogation will test the hypotheses that radiation induced translational control of gene expression is a fundamental characteristic of cellular radioresponse and that there is tumor type and/or lineage specificity in the genes subject to radiation-induced translational control. In addition, to define the molecules and processes that mediate radiation-induced translational control will be delineated. The studies will define the contribution of the general translational machinery as well as selected RNA binding proteins that have been shown to regulate the translation of specific mRNA subpopulations. Finally, the molecules mediating the process of radiation-induced translational control and the proteins corresponding to the mRNAs whose translation is affected by radiation will be tested for their role in cell survival after irradiation. These analyses, in addition to identifying fundamental determinants of radiosensitivity, will determine whether radiation-induced translational control of gene expression provides a novel source of targets for radiation modifiers. Whereas the radiobiological significance of modifying constitutively expressed proteins has been clearly established, the proposed studies offer an opportunity to investigate and potentially exploit radiation-induced translational control of gene expression, a previously unexplored component of cellular radioresponse.